Light detection and ranging (LiDAR) system using a wavelength converter

ABSTRACT

Embodiments of the disclosure provide an apparatus for emitting laser light and a system and method for detecting laser light returned from an object. The system includes a transmitter and a receiver. The transmitter includes one or more laser sources, at least one of the laser sources configured to provide a respective native laser beam having a wavelength above 1,100 nm. The transmitter also includes a wavelength converter configured to receive the native laser beams provided by the laser sources and convert the native laser beams into a converted laser beam having a wavelength below 1,100 nm. The transmitter further includes a scanner configured to emit the converted laser beam to the object in a first direction. The receiver is configured to detect a returned laser beam having a wavelength below 1,100 nm and returned from the object in a second direction.

TECHNICAL FIELD

The present disclosure relates to a Light Detection and Ranging (LiDAR)system, and more particularly to, a LiDAR system using a wavelengthconverter and method operating the same.

BACKGROUND

LiDAR systems have been widely used in autonomous driving and producinghigh-definition maps. For example, LiDAR systems measure distance to atarget by illuminating the target with pulsed laser light and measuringthe reflected pulses with a sensor. Differences in laser return timesand wavelengths can then be used to make digital three-dimensional (3-D)representations of the target. The laser light used for LiDAR scan maybe ultraviolet, visible, or near infrared. Because a narrow laser beamas the incident light from the scanner can map physical features withvery high resolution, a LiDAR system is particularly suitable forapplications such as high-definition map surveys.

However, in current LiDAR systems, the practical wavelength of the lightemitter is limited by available laser sources, photo detectors, systemperformance and laser safety requirements. The diode laser source whichcan provide wavelength range from 750 nm to 1,100 nm either doesn't haveenough power or doesn't have good beam quality in terms of collimation,especially when a small aperture is applied. Some other lasers, such asfiber laser, can provide better good beam quality and higher power. Butthe wavelength of fiber laser is normally above 1,100 nm, which cannotbe detected by silicon-based photodetector. The receivers used fordetecting laser beams having wavelengths above 1,100 nm, such asGe/InGaAs-based photodetector, usually have high cost and unsatisfactoryperformance compared with silicon-based photodetector.

Embodiments of the disclosure address the above problems by an improvedsystem for laser light emission and detection having a wavelengthconverter.

SUMMARY

Embodiments of the disclosure provide a system for detecting laser lightreturned from an object. The system includes a transmitter and areceiver. The transmitter includes one or more laser sources, at leastone of the laser sources configured to provide a respective native laserbeam having a wavelength above 1,100 nm. The transmitter also includes awavelength converter configured to receive the native laser beamsprovided by the laser sources and convert the native laser beams into aconverted laser beam having a wavelength below 1,100 nm. The transmitterfurther includes a scanner configured to emit the converted laser beamto the object in a first direction. The receiver is configured to detecta returned laser beam having a wavelength below 1,100 nm and returnedfrom the object in a second direction.

Embodiments of the disclosure also provide a system for detecting laserlight returned from an object. The system includes a transmitter and asilicon-based photodetector. The transmitter includes a plurality offiber lasers, each configured to provide a respective native laser beamhaving a respective native wavelength. The transmitter also includes awavelength converter configured to receive the native laser beamsprovided by the fiber lasers and convert the native laser beams into aconverted laser beam having a converted wavelength below any one of thenative wavelengths. The transmitter further includes a scannerconfigured to emit the converted laser beam to the object in a firstdirection. The silicon-based photodetector configured to detect areturned laser beam light having the converted wavelength and returnedfrom the object in a second direction.

Embodiments of the disclosure also provide an apparatus for emittinglaser light. The apparatus includes a plurality of fiber lasers, eachconfigured to provide a respective native laser beam having a firstwavelength. The apparatus also includes a wavelength converterconfigured to receive the native laser beams provided by the fiberlasers and convert the native laser beams into a converted laser beamhaving a second wavelength below the first wavelength. The apparatusfurther includes a scanner configured to emit the converted laser beam.

Embodiments of the disclosure further provide a method for detectinglaser light returned from an object. The method includes providing, by aplurality of laser sources, a plurality of native laser beams eachhaving a wavelength above 1,100 nm. The method also includes converting,by a wavelength converter, the native laser beams into a converted laserbeam having a wavelength below 1,100 nm. The method further includesemitting, by a scanner, the converted laser beam to the object in afirst direction. The method still further includes detecting, by areceiver, a returned laser beam having a wavelength below 1,100 nm andreturned from the object in a second direction,

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic diagram of an exemplary vehicle equippedwith a LiDAR system, according to embodiments of the disclosure.

FIG. 2 illustrates a block diagram of an exemplary LiDAR system using awavelength converter, according to embodiments of the disclosure.

FIG. 3 illustrates a block diagram of an exemplary wavelength converter,according to embodiments of the disclosure.

FIG. 4 illustrates a flowchart of an exemplary method for detectinglaser light returned from an object, according to embodiments of thedisclosure.

FIG. 5 illustrates a flowchart of an exemplary method for convertinglaser beam wavelength, according to embodiments of the disclosure.

DETAILED DESCRIPTION

Reference will now be made in detail to the exemplary embodiments,examples of which are illustrated in the accompanying drawings. Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts.

FIG. 1 illustrates a schematic diagram of an exemplary vehicle 100equipped with a LiDAR system 102, according to embodiments of thedisclosure. Consistent with some embodiments, vehicle 100 may be asurvey vehicle configured for acquiring data for constructing ahigh-definition map or 3-D buildings and city modeling. It iscontemplated that vehicle 100 may be an electric vehicle, a fuel cellvehicle, a hybrid vehicle, or a conventional internal combustion enginevehicle. Vehicle 100 may have a body 104 and at least one wheel 106.Body 104 may be any body style, such as a sports vehicle, a coupe, asedan, a pick-up truck, a station wagon, a sports utility vehicle (SUV),a minivan, or a conversion van. In some embodiments of the presentdisclosure, vehicle 100 may include a pair of front wheels and a pair ofrear wheels, as illustrated in FIG. 1. However, it is contemplated thatvehicle 100 may have less wheels or equivalent structures that enablevehicle 100 to move around. Vehicle 100 may be configured to be allwheel drive (AWD), front wheel drive (FWR), or rear wheel drive (RWD).In some embodiments of the present disclosure, vehicle 100 may beconfigured to be operated by an operator occupying the vehicle, remotelycontrolled, and/or autonomous.

As illustrated in FIG. 1, vehicle 100 may be equipped with LiDAR system102 mounted to body 104 via a mounting structure 108. Mounting structure108 may be an electro-mechanical device installed or otherwise attachedto body 104 of vehicle 100. In some embodiments of the presentdisclosure, mounting structure 108 may use screws, adhesives, or anothermounting mechanism. Vehicle 100 may be additionally equipped with asensor 110 inside or outside body 104 using any suitable mountingmechanisms. It is contemplated that the manners in which LiDAR system102 or sensor 110 can be equipped on vehicle 100 are not limited by theexample shown in FIG. 1 and may be modified depending on the types ofLiDAR system 102 and sensor 110 and/or vehicle 100 to achieve desirable3-D sensing performance.

Consistent with some embodiments, LiDAR system 102 and sensor 110 may beconfigured to capture data as vehicle 100 moves along a trajectory. Forexample, a transmitter of LiDAR system 102 is configured to scan thesurrounding and acquire point clouds. LiDAR system 102 measures distanceto a target by illuminating the target with pulsed laser light andmeasuring the reflected pulses with a receiver. The laser light used forLiDAR system 102 may be ultraviolet, visible, or near infrared. In someembodiments of the present disclosure, LiDAR system 102 may capturepoint clouds. As vehicle 100 moves along the trajectory, LiDAR system102 may continuously capture data. Each set of scene data captured at acertain time range is known as a data frame.

As illustrated in FIG. 1, vehicle 100 may be additionally equipped withsensor 110, which may include sensors used in a navigation unit, such asa Global Positioning System (GPS) receiver and one or more InertialMeasurement Unit (IMU) sensors. By combining the GPS receiver and theIMU sensor, sensor 110 can provide real-time pose information of vehicle100 as it travels, including the positions and orientations (e.g., Eulerangles) of vehicle 100 at each time stamp. In some embodiments of thepresent disclosure, pose information may be used for calibration and/orpretreatment of the point cloud data captured by LiDAR system 102.

Consistent with the present disclosure, vehicle 100 may include a localcontroller 112 inside body 104 of vehicle 100 or communicate with aremote computing device, such as a server, (not illustrated in FIG. 1)for controlling the operations of LiDAR system 102 and sensor 110. Insome embodiments of the present disclosure, controller 112 may havedifferent modules in a single device, such as an integrated circuit (IC)chip (implemented as an application-specific integrated circuit (ASIC)or a field-programmable gate array (FPGA)), or separate devices withdedicated functions. In some embodiments of the present disclosure, oneor more components of controller 112 may be located inside vehicle 100or may be alternatively in a mobile device, in the cloud, or anotherremote location. Components of controller 112 may be in an integrateddevice or distributed at different locations but communicate with eachother through a network (not shown).

FIG. 2 illustrates a block diagram of an exemplary LiDAR system 102using a wavelength converter 208, according to embodiments of thedisclosure. LiDAR system 102 may include a transmitter 202 and areceiver 204. Transmitter 202 may emit laser beams within a scan angle.Transmitter 202 may include one or more laser sources 206, wavelengthconverter 208, and a scanner 210. Consistent with the disclosure of thepresent application, wavelength converter 208 can be included intransmitter 202 to convert the laser beams of wavelength above 1,100 nmto become a laser beam of wavelength under 1,100 nm.

Using wavelength converter 208 enables LiDAR system 102 to use highpower, low divergence laser sources with silicon-based photo detector.For example, this conversion can enable the detection capability with asilicon-based photodetector 216 in receiver 204, which has a low costand improved performance compared with other types of photodetectors,such as Ge/InGaAs-based photodetector. On the other hand, with theconversion, laser sources 206 used in transmitter 202 can be high power,low divergence laser sources (even with wavelength above 1,100 nm), suchas fiber lasers, thereby improving the output laser light quality andpower. In some embodiments of the present disclosure, wavelengthconverter 208 is adaptive to various combinations of input native laserbeam number and wavelength and thus, makes the output converted laserbeam wavelength tunable.

As part of LiDAR system 102, transmitter 202 can emit a stream of pulsedlaser beams in different directions within its scan angle, asillustrated in FIG. 2. Laser sources 206 may be configured to providelaser light including one or more laser beams 207 (referred to herein as“native laser beams”) to wavelength converter 208. In some embodimentsof the present disclosure, each laser source 206 may generate a pulsedlaser beam in the ultraviolet, visible, or near infrared wavelengthrange. In some embodiments of the present disclosure, transmitter 202includes at least two laser sources 206, at least one of which is afiber laser. Fiber laser may be a laser in which the active gain mediumis an optical fiber doped with rare-earth elements, such as erbium (Er),ytterbium (Yb), neodymium (Nd), dysprosium (Dy), praseodymium (Pr),thulium (Tm), and holmium (Ho). Fiber lasers can have a high outputpower and high optical gain, such as having several kilometers longactive regions, because of fiber's high surface area to volume ratio,which allows efficient cooling. Fiber lasers can also have high opticalquality because fiber's waveguiding properties reduce or eliminatethermal distortion of the optical path, typically producing adiffraction-limited, high-quality laser beam. Depending on the dopedrare-earth elements, the wavelength of a laser beam provided by a fiberlaser may be above 1,100 nm, such as 1,047 nm, 1,053 nm, 1,062 nm, 1,064nm, 1,320 nm, 1,550 nm, between 1,570 nm and 1,600 nm, or between 1,750nm and 2,100 nm.

In some embodiments of the present disclosure, multiple laser sources206 may include at least one fiber laser. In some embodiments, multiplelaser sources 206 may further include one or more diode lasers. Diodelaser may be a semiconductor device similar to a light-emitting diode(LED) in which the laser beam is created at the diode's junction. Insome embodiments of the present disclosure, a diode laser includes a PINdiode in which the active region is in the intrinsic (I) region, and thecarriers (electrons and holes) are pumped into the active region fromthe N and P regions, respectively. Depending on the semiconductormaterials, the wavelength of a laser beam provided by a diode layer maybe smaller than 1,100 nm, such as 405 nm, between 445 nm and 465 nm,between 510 nm and 525 nm, 532 nm, 635 nm, between 650 nm and 660 nm,670 nm, 760 nm, 785 nm, 808 nm, or 848 nm.

In some embodiments of the present disclosure, no more than 3 lasersources 206 are used to maintain high wavelength conversion efficiency.In one example, transmitter 202 includes two laser sources 206, forexample, two fiber lasers, or one fiber laser and one diode laser. Inanother example, transmitter 202 includes three laser sources 206, forexample, three fiber lasers, two fiber lasers and one diode laser, orone fiber laser and two diode lasers. It is contemplated that the numberof laser sources 206 may also be larger than 3 in some embodimentsdepending on the design. Consistent with the disclosure of the presentapplication, regardless of the number of laser sources 206, at least oneof laser sources 206 is a fiber laser configured to provide native laserbeam 207 having a wavelength above 1,100 nm. In some embodiments of thepresent disclosure, all laser sources 206 (e.g., two, three or more) arefiber lasers each configured to provide native laser beam 207 having awavelength above 1,100 nm.

Wavelength converter 208 may be configured to receive the native laserbeams provided by laser sources 206 and convert native laser beams 207into a converted laser beam 209 having a wavelength below 1,100 nm. Insome embodiments of the present disclosure, at least one laser source206 is a fiber laser configured to provide native laser beam 207 havinga wavelength above 1,100 nm, and wavelength converter 208 convertsnative laser beams 207 into converted laser beam 209 having a wavelengthbelow any individual wavelength of native laser beams 207 (referred toherein as “native wavelengths”).

For example, FIG. 3 illustrates a block diagram of exemplary wavelengthconverter 208, according to embodiments of the disclosure. Wavelengthconverter 208 may include a nonlinear optical material 302 and atemperature controller 304 coupled to nonlinear optical material 302.Nonlinear optical material 302 may be configured to perform opticalfrequency mixing of native laser beams 301, 303, and 305 (e.g., examplesof native laser beams 207) having wavelengths of λ1, λ2, and λ3,respectively and output a converted laser beam 307 (an example ofconverted laser beam 209) having a wavelength of λ4. Nonlinear opticalmaterial 302 is a material that exhibits a nonlinear response ofproperties such as wavelength, polarization, phase, or path of incidentlight. The optical properties of nonlinear optical material 302 may bedependent on the degree of charge separation (polarization) induced bylight. Nonlinear optical material 302 can change the wavelength of lightpassing through it, depending upon orientation, temperature, input lightwavelength, etc. Optical frequency mixing processes that can beperformed by nonlinear optical material 302 include, but are not limitedto, second-harmonic generation (SHG)/frequency doubling, third-harmonicgeneration (THG), high-harmonic generation (HHG), sum-frequencygeneration (SFG), difference-frequency generation (DFG), opticalparametric amplification (OPA), optical parametric oscillation (OPO),optical parametric generation (OPG), spontaneous parametricdown-conversion (SPDC), and optical rectification (OR).

Nonlinear optical material 302 may include any suitable materials, suchas organic nonlinear optical materials (e.g., 2-Aminofluorene,2-Amino-3-nitropyridine, 2-Amino-5-nitropyridine,2-Chloro-3,5-dinitropyridine, 2-Chloro-4-nitroaniline, Crystal Violet,N,N′-Dimethylurea, Ethyl 4-dimethylaminobenzoate,N-Methyl-4-nitroaniline, 2-Methyl-4-nitroaniline,3-Methyl-4-nitroaniline, Nile Blue, 2-Nitroaniline, 3-Nitroaniline,4-Nitroaniline, 5-Nitroindole, 4-Nitro-3-picoline N-oxide,5-Nitrouracil, 7,7,8,8-Tetracyanoquinodimethane, and 2-Vinylnaphthalene)or inorganic nonlinear optical materials (e.g., Ammonium dihydrogenphosphate, Barium metaborate, Cesium dihydrogen arsenate, Lithiumniobium oxide, Potassium dihydrogen phosphate, Potassium niobium oxide,Sodium 1-decanesulfonate, and Lithium niobium oxide). In someembodiments of the present disclosure, nonlinear optical material 302includes a nonlinear optical crystal, such as Lithium Triborate (LBO),Beta Barium Borate (BBO), Potassium Titanyl Phosphate (KTP), PotassiumDihydrogen Phosphate & Potassium Dideuterium Phosphate (KDP & DKDP),Lithium Iodate (LiIO3), Lithium Niobate (LiNbO3), and infrared nonlinearoptical crystals (AgGaS2, AgGaSe2, GaSe, ZnGeP2).

Temperature controller 304 may be configured to set the temperature ofnonlinear optical material 302 based on the wavelength λ4 of convertedlaser beam 307. The nonlinear response of nonlinear optical material 302with respect to the wavelength λ4 of converted laser beam 307 may beaffected by the temperature of nonlinear optical material 302. In someembodiments of the present disclosure, the orientation of nonlinearoptical material 302, e.g., the plane receiving laser beams 301, 303,and/or 305 may be adjusted based on the wavelength λ4 of converted laserbeam 307 as well. In some embodiments of the present disclosure,temperature controller 304 may be part of controller 112 of vehicle 100or controlled by controller 112.

In some embodiments of the present disclosure, the wavelength λ4 ofconverted laser beam 307 is determined based on the wavelengths λ1, λ2,and λ3 of native laser beams 301, 303, and 305, respectively using thefollowing Equation (1):

$\begin{matrix}{\frac{1}{\lambda_{4}} = {\frac{1}{\lambda_{1}} + \frac{1}{\lambda_{2}} + {\frac{1}{\lambda_{3}}.}}} & (1)\end{matrix}$In some embodiments of the present disclosure, all of λ1, λ2, and λ3have a positive value. In some embodiments of the present disclosure, atleast one of λ1, λ2, and λ3 has a negative weight. In one example, oneof λ1, λ2, and λ3 has a negative value, such as λ3, so that Equation (1)becomes, for example,

$\frac{1}{\lambda_{4}} = {\frac{1}{\lambda_{1}} + \frac{1}{\lambda_{2}} - {\frac{1}{\lambda_{3}}.}}$In another example, two of λ1, λ2, and λ3 has a negative value, such asλ2 and λ3, so that Equation (1) becomes, for example,

$\frac{1}{\lambda_{4}} = {\frac{1}{\lambda_{1}} - \frac{1}{\lambda_{2}} - {\frac{1}{\lambda_{3}}.}}$

As described above, optical frequency mixing processes that can beperformed by nonlinear optical material 302 are not limited by Equation(1) and can include any suitable frequency mixing processes. In someembodiments, the laser sources include two laser sources providing twonative laser beams, respectively, and the wavelength of the convertedlaser beam is determined using the following Equation (2):

$\begin{matrix}{{\frac{1}{\lambda_{3}} = {\frac{1}{\lambda_{1}} + \frac{1}{\lambda_{2}}}},} & (2)\end{matrix}$where λ3 represents the wavelength of the converted laser beam, and λ1and λ2 each represents a respective wavelength of the two native laserbeams. In some embodiments, optical frequency mixing processes includeSHG. For example, the laser sources include one laser source providingone native laser beam, and the wavelength of the converted laser beam ishalf of a wavelength of the native laser beam. In some embodiments,optical frequency mixing processes include THG. For example, the lasersources include one laser source providing one native laser beam, andthe wavelength of the converted laser beam is a third of a wavelength ofthe native laser beam.

Referring back to FIG. 2, scanner 210 may be configured to emitconverted laser beam 209 to an object 212 in a first direction. Scanner210 may scan object 212 using converted laser beam 209 whose wavelengthis converted by wavelength converter 208 (e.g., under 1,100 nm) within ascan angle at a scan rate. Object 212 may be made of a wide range ofmaterials including, for example, non-metallic objects, rocks, rain,chemical compounds, aerosols, clouds and even single molecules. Thewavelength of converted laser beam 209 may vary based on the compositionof object 212. At each time point during the scan, scanner 210 may emitconverted laser beam 209 (incident laser light) to object 212 in adirection (incident direction) within the scan angle. In someembodiments of the present disclosure, scanner 210 may also includeoptical components (e.g., lenses, mirrors) that can focus pulsed laserlight into a narrow laser beam to increase the scan resolution and rangeof object 212.

As part of LiDAR system 102, receiver 204 may be configured to detect areturned laser beam 211 returned from object 212 in a second direction.Receiver 204 can collect laser beams returned from object 212 and outputelectrical signal reflecting the intensity of the returned laser beams.Upon contact, laser light can be reflected by object 212 viabackscattering, such as Rayleigh scattering, Mie scattering, Ramanscattering, and fluorescence. As illustrated in FIG. 2, receiver 204 mayinclude a lens 214 and a silicon-based photodetector 216. Lens 214 beconfigured to collect light from a respective direction in its field ofview (FOV). At each time point during the scan, a returned laser beam211 may be collected by lens 214. Returned laser beam 211 may bereturned from object 212 and have the same wavelength as converted laserbeam 209 (e.g., below 1,100 nm).

Silicon-based photodetector 216 may be configured to detect returnedlaser beam 211 returned from object 212 in a second direction.Silicon-based photodetector 216 may convert the laser light (e.g.,returned laser beam 211) collected by lens 214 into an electrical signal218 (e.g., a current or a voltage signal). The current is generated whenphotons are absorbed in the photodiode. Silicon-based photodetector 216may include silicon PIN photodiodes that utilize the photovoltaic effectto convert optical power into an electrical current. In some embodimentsof the present disclosure, the wavelength of laser beams that can bedetected by silicon-based photodetector 216 is below 1,100 nm, such asbetween 190 nm and 1,100 nm. In other words, silicon-based photodetector216 may not directly detect native laser beam 207 provided by lasersource 206 having a native wavelength above 1,100 nm, such as by a fiberlaser. Converted laser beam 209 (and returned laser beam 211) having aconverted wavelength below 1,100 nm, however, can be readily detected bysilicon-based photodetector 216.

FIG. 4 illustrates a flowchart of an exemplary method for detectinglaser light returned from an object, according to embodiments of thedisclosure. For example, method 400 may be implemented by LiDAR system102 in FIGS. 1-2. However, method 400 is not limited to that exemplaryembodiment. Method 400 may include steps S402-S408 as described below.It is to be appreciated that some of the steps may be optional toperform the disclosure provided herein. Further, some of the steps maybe performed simultaneously, or in a different order than shown in FIG.4.

In step S402, native laser beams 207 may be provided, by laser sources206, at least one having a wavelength above 1,100 nm (native wavelengththat has not been converted). Each native laser beam 207 may be a pulsedlaser beam in the ultraviolet, visible, or near infrared wavelengthrange. In some embodiments of the present disclosure, at least one oflaser sources 206 is a fiber laser. In one example, each laser source206 is a fiber laser. In another example, laser sources 206 include oneor more fiber lasers and one or more diode lasers. Depending on thedoped rare-earth elements, the wavelength of native laser beam 207provided by a fiber laser may be above 1,100 nm, such as 1,047 nm, 1,053nm, 1,062 nm, 1,064 nm, 1,320 nm, 1,550 nm, between 1,570 nm and 1,600nm, or between 1,750 nm and 2,100 nm. In some embodiments of the presentdisclosure, the number of laser sources 206 is not larger than 3, suchas 2 or 3.

In step S404, native laser beams 207 may be converted, by wavelengthconverter 208, into converted laser beam 209 having a convertedwavelength below 1,100 nm. In some embodiments of the presentdisclosure, the converted wavelength is determined based on the nativewavelengths of three laser sources according to Equation (1) disclosedabove. FIG. 5 illustrates a flowchart of an exemplary method 500 forconverting laser beam wavelength, according to embodiments of thedisclosure. Step S404 may be implemented using method 500. Method 500may include steps S502-S504 as described below. It is to be appreciatedthat some of the steps may be optional to perform the disclosureprovided herein. Further, some of the steps may be performedsimultaneously, or in a different order than shown in FIG. 5.

In step S502, a temperature of nonlinear optical material 302 may beset, by temperature controller 304, based on the wavelength of convertedlaser beam 209. The nonlinear response of nonlinear optical material 302with respect to the wavelength of converted laser beam 307 may beaffected by the temperature of nonlinear optical material 302. In someembodiments of the present disclosure, the orientation of nonlinearoptical material 302, e.g., the plane receiving laser beams 301, 303,and/or 305 may be adjusted based on the wavelength of converted laserbeam 307 as well.

In step S504, optical frequency mixing of native laser beams 207 may beperformed by nonlinear optical material 302. In some embodiments of thepresent disclosure, nonlinear optical material 302 includes a nonlinearoptical crystal, such as LBO, BBO, KTP, KDP & DKDP, LiIO3, LiNbO3, andinfrared nonlinear optical crystals (AgGaS2, AgGaSe2, GaSe, ZnGeP2). Insome embodiments of the present disclosure, optical frequency mixingprocesses include, but are not limited to, SHG/frequency doubling, THG,HHG, SFG, DFG, OPA, OPO, OPG, SPDC, and OR.

Referring back to FIG. 4, in step S406, converted laser beam 209 may beemitted, by scanner 210, to object 212 in a first direction (e.g.,incident direction). Object 212 may be any target in the surroundingscene of LiDAR system 102. In some embodiments of the presentdisclosure, converted laser beam 209 may be emitted within a scan angleat a scan rate as scanner 210 moves, and the first direction may bedetermined based on the position of scanner 210.

In step S408, returned laser beam 211 having a wavelength below 1,100 nmand returned from object 212 in a second direction (e.g., returndirection) may be detected by receiver 204. The wavelength of returnedlaser beam 211 may be the same as the converted wavelength (e.g., below1,100 nm). Receiver 204 may include silicon-based photodetector 216configured to convert a light signal into an electrical signal. In someembodiments of the present disclosure, silicon-based photodetector 216is capable of detecting laser beams having wavelengths below 1,100 nm,such as between 190 nm and 1,100 nm.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed system andrelated methods. Other embodiments will be apparent to those skilled inthe art from consideration of the specification and practice of thedisclosed system and related methods.

It is intended that the specification and examples be considered asexemplary only, with a true scope being indicated by the followingclaims and their equivalents.

What is claimed is:
 1. A system for detecting laser light returned froman object, comprising: a transmitter comprising: one or more lasersources, at least one of the laser sources configured to provide arespective native laser beam having a wavelength above 1,100 nm; awavelength converter configured to receive the native laser beamsprovided by the laser sources and convert the native laser beams into aconverted laser beam having a wavelength below 1,100 nm; and a scannerconfigured to emit the converted laser beam to the object in a firstdirection; and a receiver configured to detect a returned laser beamhaving a wavelength below 1,100 nm and returned from the object in asecond direction, wherein when the laser sources include two lasersources providing two native laser beams, respectively, the wavelengthof the converted laser beam is determined by$\frac{1}{\lambda_{3}} = {\frac{1}{\lambda_{2}} + \frac{1}{\lambda_{1}}}$where λ₃ represents the wavelength of the converted laser beam, and λ₁and λ₂ each represents a respective wavelength of the two native laserbeams.
 2. The system of claim 1, wherein at least one of the lasersources is a fiber laser.
 3. The system of claim 2, wherein each of thelaser sources is a fiber laser.
 4. The system of claim 3, wherein thereceiver includes a silicon-based photodetector.
 5. The system of claim3, wherein the wavelength converter comprises: a nonlinear opticalmaterial configured to perform optical frequency mixing of the nativelaser beams; and a temperature controller configured to set atemperature of the nonlinear optical material based on the wavelength ofthe converted laser beam.
 6. The system of claim 5, wherein thenonlinear optical material includes a nonlinear optical crystal.
 7. Thesystem of claim 1, wherein a number of the laser sources is not largerthan
 3. 8. The system of claim 7, wherein when the laser sources includethree laser sources providing three native laser beams, respectively,the wavelength of the converted laser beam is determined by$\frac{1}{\lambda_{4}} = {\frac{1}{\lambda_{3}} + \frac{1}{\lambda_{2}} + \frac{1}{\lambda_{1}}}$where λ₄ represents the wavelength of the converted laser beam, and λ₁,λ₂, and λ₃ each represents a respective wavelength of the three nativelaser beams.
 9. The system of claim 8, wherein at least one of λ₁, λ₂,and λ₃ has a negative weight.
 10. The system of claim 9, wherein one ofλ₁, λ₂, and λ₃ has a negative weight.
 11. The system of claim 1, whereinthe laser sources include one laser source providing one native laserbeam, and the wavelength of the converted laser beam is half of awavelength of the native laser beam.
 12. The system of claim 1, whereinthe laser sources include one laser source providing one native laserbeam, and the wavelength of the converted laser beam is a third of awavelength of the native laser beam.
 13. An apparatus for emitting laserlight, comprising: a plurality of fiber lasers, each configured toprovide a respective native laser beam having a first wavelength; awavelength converter configured to receive the native laser beamsprovided by the fiber lasers and convert the native laser beams into aconverted laser beam having a second wavelength below the firstwavelength; and a scanner configured to emit the converted laser beam,wherein the fiber lasers include three fiber lasers providing threenative laser beams, respectively, and the wavelength of the convertedlaser beam is determined by$\frac{1}{\lambda_{4}} = {\frac{1}{\lambda_{3}} + \frac{1}{\lambda_{2}} + \frac{1}{\lambda_{1}}}$where λ₄ represents the wavelength of the converted laser beam, and λ₁,λ₂, and λ₃ each represents a respective wavelength of the three nativelaser beams.
 14. The apparatus of claim 13, wherein the wavelengthconverter comprises: a nonlinear optical material configured to performoptical frequency mixing of the native laser beams; and a temperaturecontroller configured to set a temperature of the nonlinear opticalmaterial based on the wavelength of the converted laser beam.
 15. Theapparatus of claim 14, wherein the nonlinear optical material includes anonlinear optical crystal.
 16. The apparatus of claim 13, wherein thefirst wavelength is 1,100 nm.
 17. A method for detecting laser lightreturned from an object, comprising: providing, by a plurality of lasersources, a plurality of native laser beams, at least one of the laserbeams having a wavelength above 1,100 nm; converting, by a wavelengthconverter, the native laser beams into a converted laser beam having awavelength below 1,100 nm; emitting, by a scanner, the converted laserbeam to the object in a first direction; and detecting, by a receiver, areturned laser beam having a wavelength below 1,100 nm and returned fromthe object in a second direction, wherein when the laser sources includetwo laser sources providing two native laser beams, respectively, thewavelength of the converted laser beam is determined by$\frac{1}{\lambda_{3}} = {\frac{1}{\lambda_{2}} + \frac{1}{\lambda_{1}}}$where λ₃ represents the wavelength of the converted laser beam, and λ₁λ₂ each represents a respective wavelength of the two native laserbeams.
 18. The method of claim 17, wherein converting the native laserbeams into the converted laser beam comprises: setting, by a temperaturecontroller, a temperature of a nonlinear optical material based on thewavelength of the converted laser beam; and performing, by the nonlinearoptical material, optical frequency mixing of the native laser beams.